Spotlight on North American Gold & Silver Refining
Chapter 4 - Sampling and Assaying
Inspection and assay services are the bedrock upon which the metals industry builds its ability to trade with trust and confidence and can be traced back to the 1880s, when the first company opened its doors. These services are crucial in determining the precise content of precious metals, particularly in high-value and high-volume transactions involving gold and silver. The accuracy and independence of these inspections and assays are fundamental to the industry, forming the cornerstone for most mining and refining companies.
For these services to be truly effective and reliable, they must be carried out by independent entities. Whether or not accredited by LBMA, most companies involved in mining, smelting, or refining precious metals rely on independent assayers. These play a critical role in ensuring that the settlements between parties are based on accurate and trustworthy analyses.
In our survey of the largest companies within this segment of the value chain, we found that most mining and large recycling companies frequently utilise independent assay services. These services are particularly important in facilitating settlement agreements between counter-parties, ensuring that both parties have confidence in the valuation of the precious metals involved.
Moreover, some of these independent assayers also participate in LBMA’s proactive monitoring scheme, serving as approved supervisors. This involvement underscores their role as impartial arbiters in the industry, ensuring that the refiners adhere to the highest standards of accuracy and integrity in their operations.
In this segment, we explore the functions and importance of these independent assayers, particularly those who work closely with independent regulators, ensuring that the refining process remains transparent and trustworthy.
Metals Focus estimates that of the 489t / 7,539t of mined and 89t / 1,370t of recycled gold and silver respectively, the vast majority of material would be assayed or witnessed at some stage during the process of converting a doré, concentrate, sludge, or electronic waste material to a final London Good Delivery bar. In some instances, the same metal will be witnessed and assayed several times as it goes through the transformation process. In addition, these witnessing companies often act as umpire to counter-parties, offering a mechanism for quick and speedy resolution of disparate laboratory analysis.
Samplers & Assayers Active in North America
| Laboratory Company | Year Established | HQ Address | North American Office | Key Services |
|---|---|---|---|---|
| Alex Stewart International | 1978 | 2b Sefton Business Park, Aintree, Liverpool, L30 1RD, United Kingdom | Analysis, sampling, inspection and certification solutions. | |
| Alfred H Knight | 1881 | Kings Business Park, Prescot, Knowsley L34 1PJ, United Kingdom | 130 Tradd Street, Spartanburg, South Carolina,29301 | Independent inspection, analysis, and testing services |
| ALS Limited | 1978 | Caddick Road, Knowsley Business Park, Liverpool, L34 9HP, United Kingdom | Operated from the UK Office | Independent inspection/ supervison, auditing/ verification, analysis and testing services |
| Bureau Veritas | 1828 | 40-52 Boulevard du Parc, 92200 Neuilly-sur-Seine, France | 1601 Sawgrass Corporate Pkwy, Suite 400, Sunrise, FL 33323, USA | Testing, inspection, certification, consulting. |
| Intertek | 1885 | 33 Cavendish Square, London W1G 0PS, United Kingdom | 545 E. Algonquin Road, Suite L, Arlington Heights, IL 60005, USA | Quality assurance, testing, inspection, certification. |
| Ledoux & Company | 1880 | 359 Alfred Avenue, Teaneck, NJ, 07666, USA | 359 Alfred Avenue, Teaneck, NJ, 07666, USA | Chemical and physical analysis, assay services for metals, ores, and concentrates. |
| SGS | 1878 | 1 Place des Alpes, 1201 Geneva, Switzerland | 201 Rt. 17 N, Rutherford, NJ 07070, USA | Inspection, verification, testing, certification. |
Sample collection and preparation
The appointed assay company collects gold and silver samples from mining operations, refineries, or traders. Samples may include gold ore, bullion, scrap, or other forms of precious metals. Samples are carefully prepared by grinding or melting to ensure they are homogeneous before analysis. This step is crucial for obtaining accurate assay results.
Assaying techniques
While digitisation and modern laboratory methods have revolutionised the assaying process over the past 150 years, some tried and trusted techniques have endured and continue to be valued by clients in the precious metals industry. Below, we highlight a few of the most frequently requested methods for assaying gold and silver.
Fire Assay
One of the most traditional and reliable methods, fire assay involves melting the gold sample in a furnace with lead and other fluxes to separate the gold from impurities. After the process, the resulting gold or silver is weighed to determine its content in the sample. This method remains the “gold” standard for accuracy and is typically preferred by companies involved in the production, purchase, or toll treatment of doré bars. Its robustness and precision make it indispensable, particularly when the highest level of accuracy is required.
X-ray Fluorescence (XRF)
XRF is a non-destructive technique that uses X-rays to excite the atoms within a sample, allowing the machine to measure the elemental composition accurately. This method is often employed for final products like bars and jewellery, where taking a physical sample might not be possible or desirable. XRF is valued for its speed and ability to analyse the surface composition of metals without altering the sample.
Inductively Coupled Plasma (ICP)
ICP involves dissolving the gold sample in acid and analysing it with a plasma torch to detect trace metals and determine gold purity. This technique is particularly useful in scenarios where trace element analysis is essential, such as in the processing of electronic waste that contains silver and gold. ICP is favoured for its ability to provide highly detailed and accurate measurements of multiple elements within a sample, even at very low concentrations.
Atomic Absorption Spectroscopy (AAS)
AAS measures the concentration of gold in a sample by analysing the absorption of light by atoms in the sample. This technique is often used when there is a need to quantify gold content in samples with low concentrations or when analysing complex matrices. AAS is appreciated for its sensitivity and precision in detecting specific metals, making it a valuable tool in the assaying of sludges and mine waste.
Certification
There are two critical aspects of certification in the precious metals industry. The first pertains to the certificates issued by assayers upon completing their analysis, while the second involves the stringent certification standards to which the industry itself must adhere to maintain its credibility and trustworthiness.
When an assayer completes the analysis of a precious metal sample, they issue a certificate of analysis. This document details the purity and composition of the sample, typically gold, and is essential for ensuring transparency and accuracy in transactions, especially in trading and refining. The certificate serves as a verified record of the metal’s quality, which is crucial for establishing its value in the marketplace. Assay companies implement rigorous quality control protocols to ensure the reliability of their results. These measures often include the use of reference materials, conducting duplicate assays to verify consistency, and the regular calibration of analytical equipment. Such practices are vital in minimising errors and maintaining the integrity of the certification process, thereby upholding confidence in the results provided.
Assay companies themselves are subject to strict oversight, primarily through adherence to various International Organisation for Standardisation (ISO) compliance requirements. These standards are designed to ensure that assay companies operate with the highest levels of accuracy, reliability, and transparency. To comply with these standards, assay companies must maintain meticulous records of their procedures and results. This documentation is particularly important when dealing with high-value materials like gold, where even minor inaccuracies can have significant financial implications. Adherence to these industry standards not only helps in ensuring the quality of the assay process but also plays a crucial role in preserving the overall trust and credibility of the precious metals market. By integrating stringent internal quality controls and adhering to internationally recognised standards, assay companies ensure that their certifications are both reliable and respected across the industry.
Vault auditing
Gold and silver storage depositories in the US must comply with a variety of regulations to verify the physical gold they hold and may undergo regular independent audits to verify the presence and accuracy of stored metals. These audits involve physical inspections, weighing, and assaying to ensure compliance with regulatory standards.
Risk and mitigation
Performing the critical role of overseeing and verifying precious metal content, as outlined in this chapter, involves significant responsibilities and inherent risks. These include the potential for corruption and falsification of results, which can compromise the integrity of the entire process. To mitigate these risks, witnessing or supervising companies employ several strategies to maintain independence and avoid conflicts of interest. One effective approach is for mine and recycling companies to intentionally separate the roles of supervision and assaying. This separation involves hiring different entities for each task, ensuring that the supervision of the sampling process is independent of the entity conducting the assay. Additionally, a third company can be chosen to provide umpire results, serving as an impartial arbiter.
Given that many assay companies operate on-site at mines or refineries, it is crucial to maintain professional boundaries to prevent any undue influence. This is often achieved through the strict separation of duties, ensuring that no single individual or group has control over the entire process. For instance, one team may handle the sampling, while another performs the assay, and a third party supervises the overall procedure.
In the laboratory, the “four-eyes principle” is a common safeguard to ensure accuracy and prevent errors or misconduct. This principle requires that multiple individuals review and verify the results before any official report is issued. By involving multiple professionals in the process, the likelihood of bias, error, or manipulation is significantly reduced, thereby upholding the credibility of the assay results.
These practices are essential in maintaining the trust and integrity that are vital to the precious metals industry. By implementing rigorous checks and balances, assay and supervising companies can effectively manage the risks associated with their critical roles.